Constant Velocity Joint of Tripod Type

ABSTRACT

A constant velocity joint for a drive system with a first rotating shaft and a second rotating shaft, comprises: a hollow housing having an open end and a closed end and fixed to the first rotating shaft, an inner face of the housing including a plurality of guide grooves extending in an axial direction and spaced equally apart in a circumferential direction of the housing; and a tripod disposed at an end of the second rotating shaft, having a plurality of trunnions each positioned in a corresponding one of the guide grooves and being spaced equally apart in a circumferential direction of and at an angle normal to the second rotating shaft; and, an inner roller mounted to an outer end portion of each of the trunnions, an outer roller mounted on an outer face of each inner roller with needle rollers engaged between the inner and outer rollers, and allowing the outer face of each outer roller to roll and move in the corresponding one of the guide grooves and for transmitting a load between the first and second rotating shafts to drive the driving system. Each trunnion includes an a spherical surface in a circumferential area subjecting to the load, and a cylindrical protrusion disposed at the spherical surface and protruded to a distance from the at least partially spherical surface in a direction normal to the axis of the respective trunnion, the cylindrical protrusion having an spherical surface at its distal end for surface-to-surface contact with a spherical inner face of the respective inner roller while defining a gap around the cylindrical protrusion and between the spherical surface of the respective trunnion and the spherical inner face of the respective inner roller. The inner face of each inner roller may include a pair of guide grooves, preferably with an elliptical cross section, for receiving the spherical ends of the cylindrical protrusions.

REFERENCE TO RELATED APPLICATION

The present application is a continuation-in-part of U.S. patentapplication Ser. No. 11/750,138, entitled “CONSTANT VELOCITY JOINT OFTRIPOD TYPE” and filed on May 17, 2007, which was filed by the sameapplicant and assigned to the same assignee as the present application,the content of which is incorporated herein by reference in itsentirety.

FIELD OF THE INVENTION

The present invention relates to a constant velocity joint of tripodtype, which is disposed between a drive shaft and a driven shaft coupledto each other and typically used in a drive axle of, for example, anautomobile for transmitting rotational torque between the rotatingshafts.

BACKGROUND OF THE INVENTION

Tripod type constant velocity joints are well known in the automobileindustry as one type of constant velocity joints used in the drivesystem of automobiles to transfer a uniform torque and a constant speed,while operating with a wide range of joint angle. For instance, oneexample of the tripod type constant velocity joint was illustrated inJapanese Patent Application, S62-233522 as shown in FIGS. 1-2. Thistripod type constant velocity joint typically includes tripod 15 fixedto an end of the second rotating shaft, which functions as a drivenmember, and hollow cylindrical housing 13 fixed to an end of the firstrotating shaft 12 which functions as a drive member. Grooves 16 areformed at three locations on the inner face of the housing 13 at equalspacing in the circumferential direction and extend in the shaftdirection of the housing 13.

The tripod 15 comprises a boss 17 connected to the second rotating shaft14, and trunnions 18 each having a cylindrical shape and extendingradially from three locations at equal spacing around the boss 17. Eachtrunnion 18 has a roller 19 fixed at a distal end of the trunnion andwith needle rollers 20 engaged therein. In this arrangement, each roller19 can freely rotate about the trunnion 18 while also be displaced inthe axial direction of the trunnion 18. The constant velocity movementbetween the first and second rotating shafts is ensured with the rollers19 rotatably and displaceably engaging in the grooves 16 disposed alongthe inner face of the housing 13. In order to facilitate the slidingmovement, a pair of side faces 16 a are formed in circular recesses oneach side of the respective grooves 16, and each roller 19 is supportedrotatably and pivotally along the side faces 16 a of the grooves.

As the first rotating shaft 12 rotates, its rotational force istransmitted from housing 13, through roller 19, needle rollers 20,trunnions 18, and to the boss 17 of the tripod 15. This makes the boss17 rotate, and which also causes rotation of the second rotating shaft14. When the joint angle of the two rotating shafts 12 and 14 is notzero, a central axis of the first rotating shaft 12 is not aligned withthat of the second rotating shaft 14, and each of the trunnion 18displaces relative to the side face 16 a of the guide grooves 16 to movearound the tripod 15, as shown in FIG. 1 and FIG. 2. As a result, therollers 19 supported at the ends of the trunnions 18 move along theaxial directions of the trunnions 18, respectively, while rolling on theside faces 16 a of the guide grooves 16. Such movement ensures that aconstant velocity between the first and second rotating shaft isachieved.

When the first and second shafts rotate with a joint angle present, eachroller 19 moves with complexity. For example, each roller 19 moves inthe axial direction of the housing 13 along each of the side faces 16 aof the respective guide grooves 16, while the rollers 19 change inorientation and further displace in the axial direction of the trunnion18. Such movement of the rollers 19 cannot cause a relative movementbetween a peripheral outside face of each of the rollers 19 and each ofthe side faces 16 a to be smoothly made. Thus, a relatively largefriction occurs between the faces. As a result, this tripod typeconstant velocity joint produces three-directional axial forces as theshafts rotate. In the application of a tripod joint to the vehicles, itis known that the axial forces may cause a transverse vibrationtypically referred to as “shudder”, if a large torque is transmittedwith a relatively large joint angle present.

In order to restrain such a shudder problem from occurring, FR 275280discloses a structure as shown in FIG. 3, and U.S. Pat. No. 6,533,668 B2discloses a structure as shown in FIG. 4. In the structure shown in FIG.3( a), roller 19 a is guided parallel to the housing groove andspherical trunnion 18 can swing and pivot around an inner sphericalroller surface of inner roller 19 b. In this case, the contact areabetween the inner spherical surface of the inner roller 19 b and thetrunnion 18, when receiving torque for a load, is of an elliptical shapeas shown in FIG. 3( b). It has a longer contact diameter “a” and ashorter contact diameter “b”, because a radius “r” of a longitudinalcross-sectional shape of the spherical trunnion 18 is smaller than aradius “r3” of the trunnion 18.

The trunnion and roller structure shown in FIG. 4 has a structuresimilar to that shown in FIG. 3, however, with certain modificationsthereof. The trunnion 18′ has an elliptical shape in the cross sectionalview taken normal to the trunnion axis, which comprises a shorterdiameter “B” in the length not receiving a load, and a longer diameter“A” in the length for receiving a load. This is to make a contactpattern between the inner spherical surface of the inner roller 19 b andthe trunnion 18′ closer to a circle, when receiving a torque for a load.As a result, a longer contact diameter a′ in FIG. 4 becomes smaller thanthe longer contact diameter a in FIG. 3 due to the elliptical shape ofthe trunnion 18′. However, it still has an elliptical contact patterneven though the degree of ellipse becomes less than that shown in FIG. 3because a curvature of a longitudinal cross-section of the trunnion 18′formed by radius r2 and R is not equal to a curvature of an axialcross-section of the trunnion 18 formed by an ellipse 18 a defined as alonger diameter A and a shorter diameter B.

Moreover, for manufacturing the constant velocity joint of FIG. 4, thereare considerable difficulties not only to machine a complex sphericalsurface defined by a curvature of a longitudinal cross-section of thetrunnion 18′ formed by radius r2 and R and the ellipse shape 18′ definedas a longer diameter A and a shorter diameter B, but also to measure thetrunnion 18′ having a complex three dimensional profile, in terms ofboth inspection and quality control. These difficulties cause thecontact pattern mentioned above to be inconsistent in terms of quality,which leads to high costs in manufacturing perspective and also topotential quality control issues.

When these conventional joints rotate with a joint angle present uponreceiving loads, as shown in FIG. 3( b) and FIG. 4( b), a pivotalmovement of counterclockwise direction of trunnion 18 and 18′ causes apivotal sliding action to take place on the contact ellipse. Then thepivotal sliding action operates as a frictional spinning moment (of adirection indicated by arrows “Ts” in FIG. 3( b)) so as to change arolling direction of the roller assembly 19, which comprises the innerroller 19 b and the outer roller 19 a with needle bearings 20 engagedthere-between. As a result, direction of the roller assembly 19 changesand it is in contact with inner or outer face of the guide groove 16,and thus, increasing a frictional contact force there-between. Moreover,the roller assembly 19 displaces not to parallel to the guide groove 16.Hence it is difficult for the roller assembly 19 to be smoothly rolled,and causes a significant rolling resistance.

Moreover, in order to provide grease-entry space for better durabilityand smooth operation, space “s” is provided between the lower end at theinner face of the inner roller 19 b and the spherical face of thetrunnion 18, as shown in FIG. 3( a). Alternatively, space “s” can alsobe provided between the upper and lower ends at the inner face of theinner roller 19 b and the upper and lower portions of the spherical faceof the trunnion 18, as shown in FIG. 4( a). However, sufficient greasecannot permeate into the space of the upper end between the inner roller19 b and the trunnion 18 easily, in the structure shown in FIG. 3 andFIG. 4. In the case shown in FIG. 3, space is not provided to the upperend of the trunnion, even in the axial direction thereof, and space inthe circumferential direction is smaller than that in the axialdirection, due to an ellipse contact in which a longer contact diameter“a” in the circumferential direction is bigger than a shorter diameter“b” in the axial direction, thereby blocking grease from the contactarea by the difference of the longer contact diameter and the shorterdiameter, especially in terms of the circumferential direction, in thestructures shown both in FIG. 3 and FIG. 4. As such, because the spaceis too narrow to accommodate sufficient grease in the circumferentialand axial direction, it is difficult for the grease to be introducedinto the space. This becomes more problematic when the grease is in highdensity condition, for example, during the initial driving stage ofautomobile particularly at a cold outside temperature, which causes asignificant rolling resistance in the drive system.

A clearance can be provided between the needle roller 20 and the outerroller 19 a and the inner roller 19 b, all in the radial direction andin the circumferential direction to reduce the rolling resistance.However, the clearance is not sufficient to facilitate the grease topenetrate between the needle roller 20 and the outer roller 19 a and theinner roller 19 b, because rims 19 a 1 and 19 a 2 inwardly protruded atboth circumferential ends of the outer roller 19 a block the grease fromflowing between the needle roller 20, the outer roller 19 a and theinner roller 19 b. This inadequate greasing condition causes the needlerollers 20 not to be rolled smoothly between the inner roller 19 b andthe outer roller 19 a.

SUMMARY OF THE INVENTION

One object of the present invention is to provide a tripod type constantvelocity joint which has a simple and durable structure and also iseffective and reliable in operation, in which the joint includes, amongother members, plural (e.g., three) trunnions each having a pair ofcylindrical protrusions protruded a predetermined distance from theouter surface of the trunnion in a direction generally perpendicular tothe axis of the corresponding trunnion. These cylindrical protrusionsprovide a reduced contact surface between the trunnion and the innerface of the corresponding inner roller, and thus, reducing thefrictional spinning force acting on the contact ellipse made between theouter face of the trunnion and the inner face of the inner roller, dueto the pivotal sliding movement of the trunnion axis known in the art.

Another object of the present invention is to provide a tripod typeconstant velocity joint having a sufficient lubrication mechanismbetween the inner race and the trunnion, and between the outer roller,the needle rollers, and the inner roller, to minimize the rollingresistance when rotating with any joint angle present.

A further object of the present invention is to provide a tripod typeconstant velocity joint which as a reliable structure and easy to beassembled. The joint includes, among other members, plural trunnionseach having a pair of opposing cylindrical protrusions each protruded apredetermined distance from the outer surface of the trunnion in adirection generally perpendicular to the axis of the correspondingtrunnion and each having spherical outer surface, and a pair of groovesformed on the bottom portion of the inner roller at two opposinglocations corresponding to the pair of cylindrical protrusions tofacilitate assembling the trunnion to the inner roller through thegrooves. In certain preferred embodiments, each of the two opposingbottom grooves of the inner roller has an elliptical shape which canfacilitate assembling the inner roller into the trunnion as the assemblyis made with the inner roller tilted to a predetermined degree. This isbecause the elliptical shape of the two opposing bottom grooves of theinner roller corresponds to the outer surface of the two opposingprotrusions of the trunnion when they are tilted with respect to eachother as the spherical outer surface of the protrusions is projected toan elliptical shape when viewed from the tilted angle of the innerroller. This particular arrangement can reduce stress-concentrationstypically occurring at the edge portions of the bottom grooves of theinner roller during the assembly process, and thus, can also prevent apotential plastic deformation of the inner roller during the assemblyprocess of pressing the trunnion into the inner roller. As a result, anextra manufacturing or tooling cost, typically required for theassembly, can be reduced.

To solve the above described problems and other problems to berecognized by following disclosure, a tripod type constant velocityjoint is provided for a drive system, the drive system including firstand second rotating shafts coupled with the constant velocity joint, inwhich the constant velocity joint comprises: a hollow housing having anopening at one end, and a closing at its opposite end fixed to an end ofthe first rotating shaft, an inner face of the housing including aplurality of guide grooves extending in an axial direction of thehousing and spaced equally apart in a circumferential direction of thehousing, each groove having a pair of side faces opposing to each other;and a tripod disposed at an end of the second rotating shaft, having aplurality of trunnions each positioned in a corresponding one of theguide grooves and being spaced equally apart in a circumferentialdirection of and at an angle normal to the second rotating shaft; and,an inner roller mounted to an outer end portion of each of thetrunnions, an outer roller mounted on an outer face of each inner rollerwith needle rollers engaged between the inner and outer rollers, andallowing the outer face of each outer roller to roll and move in thecorresponding one of the guide grooves and for transmitting a loadbetween the first and second rotating shafts to drive the drivingsystem.

Each of the trunnions includes an at least partially spherical surfacein a circumferential area subjecting to the load, and a cylindricalprotrusion disposed at the at least partially spherical surface andprotruded to a distance from the at least partially spherical surface ina direction normal to the axis of the respective trunnion, thecylindrical protrusion having an at least partially spherical surface atits distal end for surface-to-surface contact with an at least partiallyspherical inner face of the respective inner roller while defining a gaparound the cylindrical protrusion and between the at least partiallyspherical surface of the respective trunnion and the at least partiallyspherical inner face of the respective inner roller, the gap around thecylindrical protrusion of the respective trunnion allowing a lubricantto introduce in the gap for lubrication.

Each of the trunnions preferably includes a flat surface in acircumferential area not subjecting to the load and thereby providinglarger space between the flat surface and the at least partiallyspherical inner face of the respective inner roller, the space allowinga lubricant to introduce therein for lubrication.

Each of the inner rollers preferably includes a pair of grooves eachformed on the bottom portion of the respective inner roller facing aboss of the tripod, and further includes another pair of grooves eachformed on the top portion of the respective inner roller, wherein therespective inner roller is elastically deformable about the pair ofgrooves formed on the top portion of the inner roller to expand theinner opening of the inner roller to install the corresponding trunnionin the inner roller.

The cylindrical protrusion has a cross section of circular shape, oralternatively, of elliptical shape. Each of the trunnions may have acentral portion recessed or cut out from said cylindrical protrusion forreducing a contact area between the inner rollers and trunnions.

According to another aspect of the invention, a method of assembling aroller assembly of a constant velocity joint on a trunnion of the joint,comprises the steps of:

providing a roller assembly for a constant velocity joint, the rollerassembly including: an outer roller with a tapered cylindrical surfaceformed on the inner face of the outer roller; an inner roller with atapered cylindrical surface formed on the outer face of the inner rollerand with at least partially spherical inner face, the tapered outercylindrical surface of the inner roller having a same taper angle withthe tapered inner cylindrical surface of the outer roller, the innerroller including a pair of grooves formed on a bottom portion of theinner roller facing a boss of the trunnion and in a diametric direction,and another pair of grooves formed on a top portion of the inner rollerand in a diametric direction perpendicular to the direction of the pairof grooves formed on the bottom portion; and needle rollers forreceiving between the inner and outer rollers;

providing a constant velocity joint having a tripod with at least onetrunnion, the trunnion including a pair of cylindrical protrusionsprotruded normal to the axis of the trunnion to a predetermined heightfrom an outer surface of the trunnion, each of the cylindricalprotrusions having a generally spherical end surface for contacting withthe at least partially spherical inner face of the inner roller;

mounting the outer roller on a shoulder portion of the tripod disposedbelow the trunnion, in such a manner that the tapered inner cylindricalsurface of the outer roller is converged in a radial direction facing aboss of the tripod, the outer roller having the needle rollers assembledin the tapered inner cylindrical surface of the outer roller;

placing the inner roller in an opening defined by the needle rollersassembled in the outer roller with the pair of cylindrical protrusionsreceived in the pair of grooves on the bottom of the inner roller, insuch a manner that a tapered cylindrical surface formed on the outerface of the inner roller are converged in the radial direction facingthe boss and the pair of grooves on the top portion of the inner raceare positioned in the direction not receiving the load; and

applying a gripping force on the upper edges of the inner roller in thedirection receiving the load, and forcing the inner opening of the innerroller elastically expanded around the grooves formed on the top portionof the inner roller and in the direction receiving the load, the elasticexpansion being within a radial clearance of the roller assemblyprovided between the tapered cylindrical outer face of the inner roller,the tapered cylindrical inner face of the outer roller, and the needlerollers, and thereby mounting the inner roller to the trunion with thegenerally spherical end surface of the cylindrical protrusionscontacting against the at least partially spherical inner face of theinner roller.

According to another aspect of the invention, a method of assembling aroller assembly of a constant velocity joint on a trunnion of the joint,comprises the steps of:

providing a roller assembly for a constant velocity joint, the rollerassembly including: an outer roller with a tapered cylindrical surfaceformed on the inner face of the outer roller; an inner roller with atapered cylindrical surface formed on the outer face of the inner rollerand with at least partially spherical inner face, the tapered outercylindrical surface of the inner roller having a same taper angle withthe tapered inner cylindrical surface of the outer roller, the innerroller including a pair of grooves formed on a bottom portion of theinner roller facing a boss of the trunnion and in a diametric direction,and another pair of grooves formed on a top portion of the inner rollerand in a diametric direction parallel to the direction of the pair ofgrooves formed on the bottom portion; and needle rollers for receivingbetween the inner and outer rollers;

providing a constant velocity joint having a tripod with at least onetrunnion, the trunnion including a pair of cylindrical protrusionsprotruded normal to the axis of the trunnion to a predetermined heightfrom an outer surface of the trunnion, each of the cylindricalprotrusions having a generally spherical end surface for contacting withthe at least partially spherical inner face of the inner roller;

mounting the outer roller on a shoulder portion of the tripod disposedbelow the trunnion, in such a manner that the tapered inner cylindricalsurface of the outer roller is converged in a radial direction facing aboss of the tripod, the outer roller having the needle rollers assembledin the tapered inner cylindrical surface of the outer roller;

placing the inner roller in an opening defined by the needle rollersassembled in the outer roller with the pair of cylindrical protrusionsreceived in the pair of grooves on the bottom of the inner roller, insuch a manner that a tapered cylindrical surface formed on the outerface of the inner roller are converged in the radial direction facingthe boss and the pair of grooves on the top portion of the inner raceare positioned in the direction receiving the load; and

applying a gripping force on the upper edges of the inner roller in thedirection not receiving the load, and forcing the inner opening of theinner roller elastically expanded around the grooves formed on the topportion of the inner roller and in the direction not receiving the load,the elastic expansion being within a radial clearance of the rollerassembly provided between the tapered cylindrical outer face of theinner roller, the tapered cylindrical inner face of the outer roller,and the needle rollers, and thereby mounting the inner roller to thetrunion with the generally spherical end surface of the cylindricalprotrusions contacting against the at least partially spherical innerface of the inner roller.

According to a further aspect of the invention, a method of assembling aroller assembly of a constant velocity joint on a trunnion of the joint,comprises the steps of:

providing a roller assembly for a constant velocity joint, the rollerassembly including: an outer roller with a tapered cylindrical surfaceformed on the inner face of the outer roller; an inner roller with atapered cylindrical surface formed on the outer face of the inner rollerand with at least partially spherical inner face, the tapered outercylindrical surface of the inner roller having a same taper angle withthe tapered inner cylindrical surface of the outer roller, the innerroller including a pair of grooves formed on a bottom portion of theinner roller facing a boss of the trunnion and in a diametric direction,and two pairs of grooves formed on a top portion of the inner rollerboth in a diametric direction parallel to and in a diametric directionperpendicular to the direction of the pair of grooves formed on the topportion; and needle rollers for receiving between the inner and outerrollers;

providing a constant velocity joint having a tripod with at least onetrunnion, the trunnion including a pair of cylindrical protrusionsprotruded normal to the axis of the trunnion to a predetermined heightfrom an outer surface of the trunnion, each of the cylindricalprotrusions having a generally spherical end surface for contacting withthe at least partially spherical inner face of the inner roller;

mounting the outer roller on a shoulder portion of the tripod disposedbelow the trunnion, in such a manner that the tapered inner cylindricalsurface of the outer roller is converged in a radial direction facing aboss of the tripod, the outer roller having the needle rollers assembledin the tapered inner cylindrical surface of the outer roller;

placing the inner roller in an opening defined by the needle rollersassembled in the outer roller with the pair of cylindrical protrusionsreceived in the pair of grooves on the bottom of the inner roller, insuch a manner that a tapered cylindrical surface formed on the outerface of the inner roller are converged in the radial direction facingthe boss and said one pair of grooves on the top portion of the innerrace are positioned in the direction not receiving the load and said theother pair of grooves on the top portion of the inner race arepositioned in the direction receiving the load; and

pressing the inner roller into the trunnion by a force applied in theaxial direction of the trunnion, and forcing the inner opening of theinner roller elastically expanded around said two pairs of groovesformed on the top portion of the inner roller both in the directionreceiving the load and in the direction not receiving the load, theelastic expansion being within a radial clearance of the roller assemblyprovided between the tapered cylindrical outer face of the inner roller,the tapered cylindrical inner face of the outer roller, and the needlerollers, and thereby mounting the inner roller to the trunion with thegenerally spherical end surface of the cylindrical protrusionscontacting against the at least partially spherical inner face of theinner roller.

According to the invention as disclosed, the contact area fortransmitting torque is between the inner spherical face of the innerroller and a spherical end surface of the cylindrical protrusionsprotruded along the axis normal to the axis of the trunnion, and has acircular shape. This circular contact area can significantly reducefluctuations or shudder problems in the drive system during rotationwhich can be caused by the frictional spinning moment owing to theelliptical contact area in the conventional constant velocity jointknown in the art.

The contact made in transmitting torque between the tapered cylindricalouter face of the inner roller and needle rollers and the taperedcylindrical inner face of the outer roller forces the roller assembly tobe pressed to the bottom portion of the groove guides of the housingfacing a boss of the trunnion, by an axial component of a load which isacting in the direction of the axis of the trunnion and at the same timefacing a boss of the trunnion. Thus it is possible to help the rollerassembly to rotate smoothly and without any significant fluctuationduring rotation.

More space is provided between the inner face of the inner roller andthe trunnion in a circumferential direction as well as in the axialdirection, by adopting a cylindrical protrusion having a sphericalsurface at its end and is positioned to the direction of receiving aload. This configuration enables grease to flow smoothly into and out ofthe space provided in the circumferential and axial direction which issecured by a height of a cylindrical protrusion projected from thetrunnion and by its cross-section.

More clearance is provided between the needle roller and the inner faceof the outer roller and the outer face of the inner roller, in theradial and the circumferential direction, by providing a taperedcylindrical face to both the inner face of the outer roller and theouter face of the inner roller, which clearance in a top portion betweenthe needle rollers and the inner roller and the outer roller is biggerthan that in a bottom portion facing a boss of the tripod, both in theradial direction and in the circumferential direction. Thus, moreclearance in the top portion makes grease flow easily in the joint andfacilitates an initial lubrication to the roller assembly. Accordingly,the invention can bring about advantages including a stable rolling ofthe roller assembly, a smaller rolling resistance, and a lower axialforce of the joint.

According to a further aspect of the invention, a tripod type constantvelocity joint for a drive system having a first rotating shaft and asecond rotating shaft coupled with the constant velocity joint,comprises: a hollow housing having an opening at one end, and a closingat its opposite end fixed to an end of the first rotating shaft, aninner face of the housing including a plurality of guide groovesextending in an axial direction of the housing and spaced equally apartin a circumferential direction of the housing, each groove having a pairof side faces opposing to each other; a tripod disposed at an end of thesecond rotating shaft, having a plurality of trunnions each positionedin a corresponding one of the guide grooves and being spaced equallyapart in a circumferential direction of and at an angle normal to thesecond rotating shaft; and, an inner roller having a spherical innerface for receiving an outer end portion of each of the trunnionstherein, an outer roller mounted on an outer face of each inner rollerwith needle rollers engaged between the inner and outer rollers, andallowing the outer face of each outer roller to roll and move in thecorresponding one of the guide grooves and for transmitting a loadbetween the first and second rotating shafts to drive the drivingsystem; wherein each of the trunnions includes a pair of cylindricalprotrusions opposingly disposed and protruded to a distance from anouter surface of the trunnion in a direction normal to the axis of thetrunnion, each of the cylindrical protrusions including a sphericalsurface at its distal end for surface-to-surface contact with thespherical inner face of the inner roller while defining a gap around thecylindrical protrusion and between the surface of the trunnion and thespherical inner face of the inner roller; and wherein each of the innerrollers includes a pair of grooves each formed in a diametric directionand on the bottom portion of the inner roller facing a boss of thetripod, the pair of grooves sized for receiving the pair of cylindricalprotrusions of the trunnion while inclining the inner roller to apredetermined degree with respect to the trunnion for assembly.

Each of the pair of grooves formed on the bottom portion of the innerroller preferably has an elliptical groove shape corresponding to anelliptical shape of the pair of cylindrical protrusions when projectedfrom the inner roller inclined to the predetermined degree with respectto the trunnion. The cylindrical protrusions of the trunnions arepreferably configured and dimensioned that they can be securely receivedin the elliptical grooves such that, after assembly, they can not bepulled out of the grooves under a normal operating condition because thecylindrical protrusions have a height larger than the depth of thebottom grooves of the inner roller.

Alternatively, each of the grooves formed on the bottom portion of theinner roller may comprises a central circular groove portion and twoperipheral groove portions disposed lateral to the central circulargroove portion, in which the central circular groove portion has aradius defined by the elliptically projected surface size of thecylindrical protrusions and the two peripheral groove portions aregenerally planar with a taper angle tangential to the ellipticallyprojected surface of the cylindrical protrusions.

According to a further aspect of the invention, a method of assembling aroller assembly of a constant velocity joint onto a trunnion of thejoint, comprises the steps of:

providing a roller assembly for a constant velocity joint, the rollerassembly including: an outer roller with a tapered cylindrical surfaceformed on the inner face of the outer roller, an inner roller with atapered cylindrical surface formed on the outer face of the inner rollerand with at least partially spherical inner face, the tapered outercylindrical surface of the inner roller having a same taper angle withthe tapered inner cylindrical surface of the outer roller, the innerroller including a pair of grooves diametrically disposed on a bottomportion of the inner face of the inner roller, and needle rollers forreceiving between the inner and outer rollers;

providing a constant velocity joint having a tripod with at least onetrunnion, the trunnion including a pair of cylindrical protrusionsprotruded normal to the axis of the trunnion to a predetermined heightfrom an outer surface of the trunnion, each of the cylindricalprotrusions having a generally spherical end surface for contacting withthe at least partially spherical inner face of the inner roller;

mounting the outer roller on a shoulder portion of the tripod disposedbelow the trunnion in such a manner that the tapered inner cylindricalsurface of the outer roller is converged in a radial direction facing aboss of the tripod, the outer roller having the needle rollers assembledin the tapered inner cylindrical surface of the outer roller;

placing the inner roller onto the trunnion and partially introducing thepair of cylindrical protrusions of the trunnion in the correspondingpair of grooves formed on the bottom portion of the inner roller;

tilting the inner and outer rollers with one side of the outer rollerabuts against the shoulder portion of the trunnion such that one of thepair of cylindrical protrusions is thoroughly received in the inner faceof the inner roller through a corresponding one of the pair of groovesof the inner roller and the other one of the pair of cylindricalprotrusions is still partially introduced in the other one of the pairof grooves of the inner roller, and allowing the inner and outer rollersto be inclined by a predetermined degree with respect to the trunnion;and

pushing an upper side of the inclined outer roller down to the shoulderportion of the trunnion until the other one of the pair of cylindricalprotrusions is completely received in the inner face of the inner rollerthrough the other one of the pair of grooves of the inner roller.

In one preferred embodiment, said providing the roller assembly step andsaid providing the constant velocity joint step provide the inner rollerhaving the pair of grooves each with an axial length smaller than adistance from the bottom face of the inner roller to the center line ofthe inner roller, and also provide the trunnion having the pair ofcylindrical protrusions with a distance between the two spherical endsurfaces of the pair of cylindrical protrusions larger than an openingsize between the pair of grooves and with a distance between the twospherical end surfaces of the pair of cylindrical protrusions, whenprojected from the axis of the inner roller inclined by said tiltingstep, still larger than the opening size between the pair of grooves;and wherein said pushing step is performed while applying a force ofpredetermined amount on the upper side of the inclined outer roller witha lower side of the inclined outer roller abutting against the shoulderportion of the trunnion for allowing an elastic expansion of the innerroller for assembly.

In another preferred embodiment, said providing the roller assembly stepand said providing the constant velocity joint step provide the innerroller having the pair of grooves each with an axial length about thesame as a distance from the bottom face of the inner roller to thecenter line of the inner roller, and provide the trunnion having thepair of cylindrical protrusions with a distance between the twospherical end surfaces of the pair of cylindrical protrusions about thesame as an opening size between the pair of grooves and with a distancebetween the two spherical end surfaces of the pair of cylindricalprotrusions, when projected from the axis of the inner roller inclinedby said tilting step, smaller than the opening size between the pair ofgrooves; and wherein said pushing step is performed without applying anexternal force of considerable amount on the upper side of the inclinedouter roller with a lower side of the inclined outer roller abuttingagainst the shoulder portion of the trunnion for assembly.

In another preferred embodiment, said providing the roller assembly stepand said providing the constant velocity joint step provide the innerroller having the pair of grooves each with an axial length smaller thana distance from the bottom face of the inner roller to the center lineof the inner roller, and provide the trunnion having the pair ofcylindrical protrusions with a distance between the two spherical endsurfaces of the pair of cylindrical protrusions larger than an openingsize between the pair of grooves and with a distance between the twospherical end surfaces of the pair of cylindrical protrusions, whenprojected from the axis of the inner roller inclined by said tiltingstep, about the same as the opening size between the pair of grooves;and wherein said pushing step is performed without applying an externalforce of considerable amount on the upper side of the inclined outerroller with a lower side of the inclined outer roller abutting againstthe shoulder portion of the trunnion for assembly.

BRIEF DESCRIPTION OF THE DRAWINGS

The above described and other objects, features and advantages of thepresent invention will be more apparent from the presently preferredembodiments of the invention disclosed in the following description andillustrated in the accompanying drawings, in which:

FIG. 1 shows a perspective view of a conventional tripod type constantvelocity joint.

FIG. 2 shows a side cross-sectional view of a conventional tripod typeconstant velocity joint.

FIG. 3( a) is an explanatory view showing a relationship regarding thelocation of a conventional axis and inner roller.

FIG. 3( b) is an explanatory view showing a frictional spinning momentgenerated in a conventional tripod type constant velocity joint.

FIG. 4( a) shows both a cross-sectional view of a trunnion and a partiallongitudinal cross-sectional view of the trunnion and the inner roller,according to a conventional tripod type constant velocity joint.

FIG. 4( b) shows an explanatory view showing a frictional spinningmoment generated in a conventional tripod type constant velocity joint.

FIGS. 5( a) and 5(b) are cross-sectional views showing the firstembodiment of the present invention, in which FIG. 5( a) is alongitudinal cross-sectional view and FIG. 5( b) is a sidecross-sectional view.

FIGS. 6( a) and 6(b) are cross-sectional views of the trunnionillustrating the second embodiment of the present invention, in whichFIG. 6( a) is a view of an axis of receiving a load, and FIG. 6( a) is aview of an axis of non-receiving a load.

FIGS. 7( a) and 7(b) are cross-sectional views of the trunnion showingthe third embodiment of the present invention, in which FIG. 7( a) is aview of an axis of receiving a load, and FIG. 7( b) is a view of an axisof non-receiving a load.

FIGS. 8( a) and 8(b) are cross-sectional views of the trunnion showingthe fourth embodiment of the present invention, in which FIG. 8( a) is aview of an axis of receiving a load, and FIG. 8( b) is a view of an axisof non-receiving a load.

FIGS. 9( a)-9(c) are cross-sectional views of the inner roller showingthe fifth embodiment of the present invention, in which FIG. 9( a) is atop view, FIG. 9( b) is a side view, and FIG. 9( c) is a bottom view.

FIG. 10 is a cross-sectional view of the outer roller showing the sixthembodiment of the present invention.

FIG. 11 is an explanatory view showing a load force acting on the rollerassembly.

FIG. 12 and FIG. 13 are cross-sectional views of the seventh embodimentof the present invention, in which FIG. 12 shows an explanatory viewshowing an arrangement made between the roller assembly and the trunnionbefore fitting the roller assembly into the trunnion, and FIG. 13 is anexplanatory view showing how to get the roller assembly into thetrunnion, based on an arrangement shown in FIG. 12.

FIG. 14 and FIG. 15 are cross-sectional views of the eighth embodimentof the present invention, in which FIG. 14 shows an explanatory viewshowing an arrangement made between the roller assembly and the trunnionbefore fitting the roller assembly into the trunnion, and FIG. 15 is anexplanatory view showing how to get the roller assembly into thetrunnion, based on an arrangement shown in FIG. 14.

FIG. 16 and FIG. 17 are cross-sectional views of the ninth embodiment ofthe present invention, in which FIG. 16 shows an explanatory viewshowing an arrangement made between the roller assembly and the trunnionbefore fitting the roller assembly into the trunnion, and FIG. 17 is anexplanatory view showing how to get the roller assembly into thetrunnion, based on an arrangement shown in FIG. 16.

FIG. 18 is a cross-sectional view showing the tenth embodiment of thepresent invention.

FIG. 19 shows the eleventh embodiment; in which FIG. 19( a) is alongitudinal cross-sectional view at a joint angle and FIG. 19( b) is aside cross-sectional view, and FIG. 19( c) is an explanatory viewshowing the inner face of the outer roller and needle rollers.

FIG. 20 a cross-sectional view illustrating the twelfth embodiment ofthe present invention.

FIGS. 21( a)-21(f) are cross-sectional and explanatory views of thetwelfth embodiment of the present invention, in which FIG. 21( a) is apartial cross-sectional view illustrating a spatial relationship betweenthe trunnion and the inner roller with the inner roller inclined by theangle Ω, FIG. 21( b) is a partial view illustrating the ellipticalprojections of the circular shapes of the cylindrical protrusions whenviewed from the angle of the inner roller tilted by the angle Ω, FIG.21( c) is partial views of the inner roller and trunnion shown from thedirection M in FIG. 21( a), FIG. 21( d) is cross sectional views of theinner roller, and FIG. 21( e) is a partial cross-sectional viewillustrating the state that the inner roller is assembled into thetrunnion, and FIG. 21( f) is partial views of the inner roller andtrunnion shown from the direction N in FIG. 21( e) in which the rightside figure shows a partial view enlarged from the left side figure forfurther illustrating the assembled state of the trunnion in the innerroller.

FIGS. 22( a)-22(c) shows the thirteenth embodiment of the presentinvention, in which FIG. 22( a) is partial views illustrating a spatialrelationship between the trunnion axis and the inner roller with theinner roller inclined by the angle Ω (in which the right side figureshows a partial view enlarged from the left side figure), FIG. 22( b) isa partial cross-sectional view of the inner roller, and FIG. 22( c) ispartial cross-sectional views showing the state that the inner roller isassembled into the trunnion (in which the right side figure shows apartial view enlarged from the left side figure).

FIGS. 23( a) and 23(b) are cross-sectional views illustrating anassembling method according to the fifteenth embodiment of the presentinvention, in which FIG. 23( a) is explanatory views illustrating apreliminary arrangement made between the roller assembly and thetrunnion before fitting the roller assembly into the trunnion, and FIG.23( b) is partial cross-sectional views illustrating a method ofassembling the roller assembly into the trunnion, performed after thearrangement shown in FIG. 23( a).

FIGS. 24( a) and 24(b) are cross-sectional views illustrating anassembling method according to the sixteenth embodiment of the presentinvention, in which FIG. 24( a) is explanatory views illustrating apreliminary arrangement made between the roller assembly and thetrunnion before fitting the roller assembly into the trunnion, and FIG.24( b) is partial cross-sectional views illustrating a method ofassembling the roller assembly into the trunnion, performed after thearrangement shown in FIG. 24( a).

FIGS. 25( a) and 25(b) are cross-sectional views illustrating anassembling method according to the seventeenth embodiment of the presentinvention, in which FIG. 25( a) is explanatory views illustrating apreliminary arrangement made between the roller assembly and thetrunnion before fitting the roller assembly into the trunnion, and FIG.25( b) is partial cross-sectional views illustrating a method ofassembling the roller assembly into the trunnion, performed after thearrangement shown in FIG. 25( a).

DETAILED DESCRIPTION OF THE INVENTION

The present application claims priority over a prior Applicant'scopending application Ser. No. 11/750,138, filed on May 17, 2007, andfurther presents updated embodiments of the invention in addition to thepreferred embodiments described in the prior application identified.

With reference to FIGS. 5-19 of the drawings, exemplary embodiments ofthe tripod type constant velocity joints of the invention and methods ofassembling the joints disclosed in application Ser. No. 11/750,138 arerepeated herein below.

FIG. 5 shows cross-sectional views of a tripod joint constant velocityjoint 1 according to the first embodiment of the present invention; inwhich FIG. 5( a) is a cross-sectional view taken vertical to the secondrotating shaft, and FIG. 5( b) is a side cross sectional view taken inan axial direction.

A tripod joint 1 shown in FIG. 5 comprises a hollow cylindrical housing2 with one end defining an opening, and the other end secured to an endof a first rotating shaft 9 serving as a drive shaft or the like, and atripod secured at one end of a second rotating shaft 8 which serves as adriven shaft or the like on the wheel side. Three grooves 10 are formedon the inner surface of the housing 2 in a configuration axiallyextending and equally spaced about the longitudinal axis of the housing.The grooves 10 are recessed from the inner surface outwardly in radialdirection of the housing 2.

A tripod 7 is secured at one end of a second rotating shaft 8 with aring-type boss 11 for supporting the tripod 7 at the second rotatingshaft 8. Three trunnions 6 are formed at three equally spaced locationsaround the boss 11 and extend outwards in a radial direction.

Each of the trunnions 6 has at least one generally flat surface 6 b in acircumferential area of the trunnion not receiving a load. Morepreferably, each trunnion 6 has two opposing flat surfaces 6 b in thecircumferential area not receiving the load, with the two flat surfacesfacing in the Z-Z direction, as shown in FIG. 5( b) and FIG. 6( b).

Each trunnion 6 has two opposing, and generally or at least partiallyspherical surfaces in the circumferential area receiving the load,namely, with the two spherical surfaces facing in the X-X direction, asshown in FIG. 5( a) and FIG. 6( a). A cylindrical protrusion 6 a isformed on each of the generally or at least partially spherical surfacesof the trunnion, with the protrusion extending outwardly (namely,extending in a direction normal to the axis of the trunnion 6) to adistance from the partially spherical surface and with the protrusionhaving a generally spherical outer surface at its distal end. Thisgenerally spherical outer surface corresponds to and insurface-to-surface contact with the generally spherical inner surface ofthe inner roller 4 of the constant velocity joint of the presentinvention.

A roller assembly 12 is mounted to each of the trunnion axes. The rollerassembly 12 is a double-roller type which has an outer roller 3, aninner roller 4, and needle rollers 5 provided between the outer andinner rollers. The inner roller 4 has a generally spherical inner facewhich is in contact with the generally spherical surfaces of thecylindrical protrusion 6 a as described above. In this manner, the twocylindrical protrusions 6 a are projected outwardly from the trunnion 6in the X-X direction of receiving the load.

The inner roller 4 has a generally cylindrical outer rolling face whichis in contact with needle rollers 5. More preferably, as shown in FIG.5( a), the cylindrical outer face of the inner roller 4 is tapered inthe rotational axis direction of the roller, and thereby, includes atapered or conical outer face 4 a with taper angle θ defined by theface.

The inner roller 4 preferably further includes two grooves 4 b on thebottom portion of the inner roller facing a boss 11, which groovesformed in the X-X direction of receiving a load as shown in FIGS. 5( a),9(a) and 9(b), in order to have the trunnion 6 assembled into the innerroller 4 through the grooves 4 b. The inner roller 4 preferably furtherincludes two grooves 4 c formed on the top portion of the inner rollerfacing the inner face 2 b of the housing, which grooves formed in theZ-Z direction of not receiving a load as shown in FIGS. 5( b), 9(a) and9(b), in order to facilitate assembly of the trunnion 6 with the innerroller 4. Owing to the presence of the top grooves 4 c, the inner roller4 can elastically be bent or deformed to a degree about the two recessedgrooves 4 c either by applying a gripping pressure inwardly on the upperrim portions 4 d (see FIG. 9( b)) of the inner roller or by forciblywidening the opening ΦH at the lower portion of the inner roller 4, orin combination of the above. This makes the distance between theopposing bottom grooves 4 b enlarged and thereby enables the assembly ofthe trunnion 6 into the inner roller 4.

The outer roller 3 has a generally spherical outer surface which is incontact with the guide grooves 2 a of the housing 2. The outer roller 3preferably includes a tapered inner face 3 a with the same taper angle θas that formed on the outer surface 4 a of the inner roller 4 withreference to the axis of the trunnion 6. More space is provided betweenthe inner face the inner roller 4 and the trunnion 6 in acircumferential direction as well as in the axial direction, by adoptinga cylindrical protrusion 6 a which is protruded along a axis normal tothe axis of the trunnion 6 and is positioned to the direction ofreceiving a load. This configuration enables grease to flow smoothly andeasily into and out of the space provided in the circumferential andaxial direction and around the cylindrical protrusion 6 a of thetrunnion 6.

More clearance Δ (as shown in FIG. 5( a)) is provided between the needlerollers 5 and the inner face of the outer roller 3 and the outer face ofthe inner roller 4 in the radial and the circumferential direction, byproviding a tapered face to both the inner face 3 a of the outer rollerand the outer face 4 a of the inner roller. The clearance in a topportion between the needle rollers and the inner roller and the outerroller is preferably bigger than that of the bottom portion facing aboss of the tripod, both in the radial direction and in thecircumferential direction, in order to make grease flow more easily inthe top portion. This configuration can facilitate an effective initiallubrication to the roller assembly.

The tripod 7 is housed in cylindrical hollow housing 2 through its openend. The inner face of the housing 2 is provided with three guidegrooves 10 (formed at locations corresponding to the roller assemblies12) which extend in the direction of the first rotational shaft 9 andare spaced apart equally in a circumferential direction of the housing2, thus the grooves 10 spaced apart from each other by about 120° aroundthe housing. Three roller assemblies 12 are rotatably and movablyreceived in their corresponding guide grooves 10 of the housing 2. Eachof the guide grooves 10 of the housing has a pair of side face 2 a and abottom portion 2 b continuously connected to the side faces 2 a. Theside faces 2 a correspond to the convex arc-shaped or generallyspherical outer face of the outer roller 3, and hence are formed as aconcave arc-shaped or generally spherical surface of approximately thesame dimension as the outer face of the outer roller 3. The side faces 2a extend in the longitudinal direction of the housing or the axialdirection of the first rotating shaft 9. Each of the bottom portions 2 bof the guide groove is provided with tracking guides (i.e., lateralguide surfaces) 2 c for guiding each of the outer rollers in securedrolling contact with an outer spherical end surface of the outer roller.In this way, the side faces 2 a of the guide grooves 10 provide atracking surface on which the outer roller can slide and roll.

According to the invention as illustrated above with preferableembodiments thereof, the contact area in transmitting torque is definedprimarily by the contact surface between the inner spherical face ofinner roller 4 and the outer spherical surface of cylindrical protrusion6 a, which is projected to a distance from the trunnion 6, and has agenerally circular shape. Thus, unlike the conventional constantvelocity joint in which its contact area has an elliptical shape asdiscussed above (FIG. 3( b)), due to its generally circular contact areabetween the trunnions and inner roller the joint of the presentinvention can significantly reduce the conventional fluctuation orshudder problem during rotation which is caused by the pivotal spinningmoment of the contact ellipse.

As illustrated in FIG. 11, the transmitting torque is transferredthrough the contact made between the tapered outer face 4 a of the innerroller 4 and needle rollers 5 and between the needle rollers 5 and thetapered inner face 3 a of the outer roller, and it causes the rollerassembly 12 to be biased toward the inner portion 2 d (i.e., toward theboss 11 of the trunnion 6) of the groove guides 10 of the housing 2, byan axial component Fv of a load which is acting in the direction of theaxis of the trunnion and toward the boss of the trunnion. Thus thisconfiguration helps the roller assembly 12 to rotate smoothly withoutany fluctuation during rotation caused by the frictional contact betweenthe lateral side of the outer roller 3 and the lateral tracking guide 2c of the housing 2.

FIG. 6 illustrates a second embodiment of the invention in which eachtrunnion 6 has a pair of cylindrical protrusions 6 a with a diameter ΦA.The two protrusions 6 a are disposed in the X-X direction of receiving aload and respectively protruded along the axis normal to the axis of thetrunnion 6 by a height H1. The two protrusions 6 a together define agenerally spherical end surface with a diameter ΦD. Each trunnion 6includes a pair of flat surfaces 6 b in the Z-Z direction of notreceiving a load, respectively, in order to diminish the spin moment andmake grease flow easily in axial and circumferential direction and forenhancing an initial lubrication of the joint.

With reference to FIG. 7, the third embodiment is described herein. Thisembodiment is similar to the first and second embodiments describedabove. The difference of this embodiment shown in FIG. 7 from the aboveembodiments is that the central portion (ΦA1) of the spherical surfaceof the cylindrical protrusion 6 a protruded from the trunnion 6 in theX-X direction of receiving a load is recessed from the surface orotherwise cut out from the trunnion, in order to reduce the contact areaformed between the inner roller and the trunnion and make grease floweasily in axial and circumferential direction and also for enhancing aninitial lubrication, thereby diminishing the spin moment in the joint.

With reference to FIG. 8, the fourth embodiment is described herein.This embodiment is also very similar to the above described embodimentas shown in FIG. 6. The difference of this embodiment from that shown inFIG. 6 is that the trunnion 6 has a cylindrical protrusion 6 a in theX-X direction of receiving the load, however, the protrusion 6 a havingan elliptical shape which defines a longer diameter B2 and shorterdiameter A2.

With reference to FIG. 9, the fifth embodiment is described herein. FIG.9 shows that the inner roller 4 has a generally spherical inner face andhas a tapered outer cylindrical face with a taper angle θ, and has twogrooves 4 b formed on the bottom portion and disposed in the X-Xdirection, in which the width “B” of each groove at the opening 4 e 1 issmaller than the width “A” at the bottom 4 e 2 of the groove. Moreover,the inner roller 4 has two recessed grooves 4 c on the top portion andin the Z-Z direction, in order to allow the distance ΦH between thegrooves 4 b to expand elastically by making the inner roller bent aroundthe two recessed grooves 4 c either by a force applied to the rims 4 dof the inner roller on the top portion or by forcing to open the inneropening ΦH of the inner roller 4. This facilitates assembly of thetrunnion into the inner roller as described above.

With reference to FIGS. 10 and 11, the sixth embodiment is describedherein. FIGS. 10 and 11 illustrate that the outer roller has a generallyspherical outer face and has a tapered inner cylindrical face having thesame taper angle θ as that formed on the outer surface of the innerroller shown in FIGS. 5 and 9, in order to force the roller assembly 12to press toward the bottom portion 2 d of the groove guides of thehousing which faces a boss 11 of the trunnion. As illustrated in FIG.11, an axial component Fv of a load F is applying in the direction ofthe axis of the trunnion and toward boss 11 (shown in FIG. 5) of thetrunnion, under a torque T acting on the joint 1, where F is T/(3*PCR),and PCR stands for pitch circle radius of the joint, Fv is an axialcomponent of F, and F′ is a resultant force of F and Fv. Thus, it ispossible to help the roller assembly 12, which is composed of the outerroller 3, the inner roller 4 and the needle rollers 5, to rotatesmoothly without any fluctuation during rotation.

Further embodiments and methods of assembly of the joint of theinvention are described herein with reference to FIGS. 12-19.

With reference to FIGS. 12 and 13, the seventh embodiment is describedherein. FIG. 12 is an explanatory view showing an arrangement madebetween the roller assembly 12 and the trunnion 6 before fitting theroller assembly 12 into the trunnion 6. The outer roller 3 is mounted onthe shoulder 11 a of a boss 11 of the tripod, in such a manner that atapered cylindrical surface 3 a on the inner face of the outer roller 3is converged in the radial direction toward boss 11 of the tripod, withthe needle rollers 5 assembled into the tapered cylindrical surface 3 aof the inner face of the outer roller 3. The inner roller 4 is placed tothe joint in a manner that cylindrical protrusions 6 a (which aredisposed in the X-X direction of receiving the load and protruded alongthe axis normal to the axis of the trunnion 6) are fitted in the twoopposing grooves 4 b on the bottom portion of the inner roller 4 in theX-X direction of receiving the load, as shown in FIG. 12, and that atapered cylindrical surface 4 a formed on the outer face of the innerroller 4 are converged in the radial direction toward the boss 11, inorder to secure some radial clearance (Δ) between the tapered outercylindrical face 4 a of the inner roller 4 and the tapered innercylindrical face 3 a of the outer roller 3 and the needle rollers 5.This configuration facilitates the assembly of the roller assembly 12with the trunnion 6. The diameter ΦA (FIG. 12( b)) of a cylindricalprotrusion 6 a with a spherical surface at its end is smaller than thewidth B of the grooves formed in the X-X direction of receiving theload, and the diameter Φd of the protruded spherical surfaces of thecylindrical protrusion 6 a disposed in the X-X direction of the trunnionis larger than the diameter ΦD of the inner roller, in order to not onlyhave the trunnion 6 assembled into the inner roller 4 through thegrooves 4 b, but also to prevent the trunnion 6 from pulling itself outfrom the inner roller 4 once they all are assembled, by a difference indimensions between the diameter Φd of the protruded spherical surfacesof the cylindrical protrusion and the diameter ΦD of the inner roller.Two grooves 4 c are recessed on its top portion of the inner face 4, andformed in the Z-Z direction of not receiving the load.

FIG. 13 illustrates a method of assembling the roller assembly 12 withthe trunnion 6, to be performed after the previous steps discussed abovein connection with FIG. 12. If a force is applied at the opposing upperedges 4 d of the inner roller 4 in the X-X direction of receiving theload, two edges 4 d get bent around the center N of the grooves 4 cformed on the top end and the trunnion 6 gets fitted into the rollerassembly 12 by making two bottom edges 4 f of the inner roller expandedin the X-X direction until ΦD becomes equal to Φd, within the radialclearance (Δ) provided among the tapered cylindrical outer face 4 a ofthe inner roller 4 and the tapered cylindrical inner face 3 a of theouter roller 3 and the needle rollers 5, as secured by the arrangementshown in FIG. 12.

With reference to FIG. 14 and FIG. 15, the eighth embodiment isdescribed, in which FIG. 14 shows an explanatory view showing anarrangement made between the roller assembly 12 and the trunnion 6before fitting the roller assembly 12 into the trunnion 6. FIG. 15 showsan explanatory view showing how to get the roller assembly 12 into thetrunnion 6, based on an arrangement shown in FIG. 14. This embodiment issimilar to the seventh embodiment shown in FIG. 12 and FIG. 13. Thedifference of this embodiment from those shown in FIG. 14 and FIG. 15 isthat the diameter ΦA of the cylindrical protrusion 6 a positioned in theX-X direction receiving the load, is larger than the width B at theopening of the grooves and the diameter Φd of the protruded sphericalsurfaces of the cylindrical protrusion 6 a positioned in the X-Xdirection is the same as the diameter ΦD of the inner roller 4, in orderto not only have the trunnion 6 assembled into the inner roller 4through the grooves 4 b, but also to prevent the trunnion 6 from pullingitself out from the inner roller 4 once they all are assembled by adifference in dimensions between the diameter ΦA of the cylindricalprotrusion 6 a and the width B at the opening of the grooves. Twogrooves 4 c 1 formed in the X-X direction are recessed on its top end ofthe inner face 4. If a force is applied at the opposing upper edges 4 d1 of the inner roller in the Z-Z direction, two edges 4 d 1 get bentaround the center N1 of the grooves 4 c 1 formed on the top end and thetrunnion 6 fits into the roller assembly 12 by making two edges 4 f ofthe bottom side of the inner roller extended in the X-X direction ofreceiving the load, until B becomes equal to or larger than ΦA, withinthe radial clearance (Δ) provided between the tapered cylindrical outerface 4 a of the inner roller 4 and the tapered cylindrical inner face 3a of the outer roller 3 and the needle rollers 5, as secured by thearrangement shown in FIG. 14.

With reference to FIG. 16 and FIG. 17, the ninth embodiment isdescribed, in which FIG. 16 shows an explanatory view showing anarrangement made between the roller assembly 12 and the trunnion 6before fitting the roller assembly 12 into the trunnion 6, and FIG. 17shows an explanatory view showing how to get the roller assembly 12 intothe trunnion 6, based on an arrangement shown in FIG. 16. Thisembodiment is a mixture of the seventh embodiment and the eighthembodiment. The difference of the present embodiment from those shown inFIG. 16 and FIG. 17 is that the roller assembly 12 is assembled from thetop into the trunnion 6 by a force applied in the axial direction of thetrunnion 6. If a force is applied on the top end of the inner roller inthe direction stated above, both edges 4 d 1 and edges 4 d get bent botharound the center N1 of the grooves 4 c 1 and around the center N of thegrooves 4 c formed on the top end of the inner roller, respectively, andthen the trunnion 6 gets fitted into the roller assembly 12 by makingtwo bottom edges 4 f of the inner roller 4 to be expanded in the X-Xdirection of receiving a load, until B becomes equal to or larger thanΦA, and at the same time until ΦD becomes equal to Φd, within the radialclearance Δ provided between the tapered cylindrical outer face 4 a ofthe inner roller 4 and the tapered cylindrical inner face 3 a of theouter roller 3 and the needle rollers 5, as secured by the arrangementshown in FIG. 16.

With reference to FIG. 18, the tenth embodiment is described herein.This embodiment is also similar to the first embodiment shown in FIG. 1.The difference of the present embodiment from that shown in FIG. 1 isthat a convex spherical surface is formed on the outer face of the outerroller 3, having the center line X1-X1 normal to the same angle θprovided to both the tapered inner cylindrical surface 3 a of the outerroller and the tapered outer cylindrical surface 4 a of the innerroller.

With reference to FIG. 19, the eleventh embodiment is described, inwhich FIG. 19( a) is a longitudinal cross-sectional view at a jointangle, FIG. 19( b) is a side cross-sectional view, and FIG. 19( c) is anexplanatory view showing the inner face of the outer roller and needlerollers. Greater spaces or gaps S1 and S2 are provided between the innerface of the inner roller 4 and the trunnion in a circumferentialdirection as well as in the axial direction, by adopting a cylindricalprotrusion 6 a positioned in the direction of receiving a load, having aspherical end surface and protruded along an axis normal to the axis ofthe trunnion. Thus, this enables grease to flow smoothly into and out ofthe space provided in the circumferential and axial direction which issecured by a height of a cylindrical protrusion projected from thetrunnion and by its shape as described above. More clearance S11 and Δare provided in between the needle roller 5 and the inner face 3 a ofthe outer roller 3 and the outer face 4 a of the inner roller 4, in theradial and the circumferential direction, by providing a taperedcylindrical face θ to both the inner face of the outer roller and theouter face of the inner roller, which clearance S11 in a top portionbetween the needle rollers and the inner roller and the outer roller isbigger than that S12 in a bottom portion facing a boss of the tripod,both in the radial direction and in the circumferential direction. Thusmore clearance in the top portion makes grease more easily flow in andhelp provide more initial lubrication to the roller assembly.

With reference now to FIGS. 20-25, further exemplary embodiments of thetripod type constant velocity joints of the invention and methods ofassembling the joints are described herein.

Referring to FIG. 20, the twelfth embodiment of the present invention isdescribed herein. Similar to the tripod type constant velocity jointsshown in FIGS. 5-19, a tripod joint 101 shown in FIG. 20 includes ahollow cylindrical housing 102 having three grooves 110 formed on theinner surface of the housing 102 and axially extending and equallyspaced about the longitudinal axis of the housing. The joint 101includes a tripod 111 which has three trunnions 106 with two cylindricalprotrusions 106 a formed at two diametrically opposing and loadreceiving locations of each trunnion 106 and extending generallyperpendicular to the axis of the trunnion 106. Each roller assemblyoperatively assembled to the respective trunnion 106 has an outer roller103, an inner roller 104, and needle rollers 105 provided between theouter and inner rollers. The outer roller 103 has a generally sphericalouter surface matching the guide grooves 102 a of the housing 102, andincludes a tapered inner face 103 a with taper angle θ defined by theface that mates with needle rollers 105. The inner roller 104 has agenerally spherical inner face which mates or corresponds to thespherical outer surface of the cylindrical protrusions 106 a, and atapered or conical outer face 104 a with the same taper angle θ as thatformed on the inner surface 103 a of the outer roller 103 with respectto the axis of the trunnion 106.

According to the present embodiment of the invention as illustrated, apair of elliptical grooves 104 b (i.e., a pair of grooves ofsemi-ellipse shape) are formed on the inner wall on the bottom portionof the inner roller 104 at two diametrically opposing areas facing aboss 107, in which the ellipse shape of the grooves has a long diameterA and a short diameter C as shown. As will be described in furtherdetails below, the elliptical-shaped grooves 104 b have a function toeffectively relieve a stress-concentration that would otherwise beoccurred during the assembly process on the edges portions of thegrooves for receiving the cylindrical protrusions 106 a, for instance,on the groove edges 4 g (see FIG. 13( b)) if the grooves have a uniformdepth as in the previous embodiments shown in FIGS. 5-19. Thus, theyfunction to reduce a potential plastic deformation of the inner roller104 that would otherwise occur during the assembly process of pressingthe cylindrical protrusions 106 a of the trunnion 106 into the innerroller 104 owing typically to an improper tooling or imprecise dimensioncontrol of inner roller 103 and/or trunnion 106. Accordingly, an extramanufacturing cost typically required for the press fitting process inthe previous embodiments can be reduced due to the two ellipticalgrooves 104 b which facilitate insertion of the trunnion 106 into theinner face of the inner roller 104 smoothly without applying anexcessive pressure, as the assembly process is performed while tiltingthe inner roller 104 about the trunnion 106 until the elliptical grooves104 b of the inner roller 104 coincide with the outer surface of thecylindrical protrusion 106 a. This is possible because the circularouter surface of each cylindrical protrusion 106 a becomes an ellipticalshape which corresponds to the corresponding elliptical groove 104 bwhen the cylindrical protrusion 106 a is projected from the tilted axisof the inner roller 104, which is described below in further details.

FIG. 21( a) illustrates a state in which the inner roller 104 withoutgrooves on the bottom portion of the roller is first placed on thecenter line X-X of the trunnion 106, and thereafter, is inclined untilthe bottom of the outer roller 103 contacts against the shoulder K ofthe boss, while the bottom edge on the inner face of the inner roller104 hangs on the top edge portion of cylindrical protrusion 106 a. FIGS.21( b) and 21(c) illustrate that both the inner race 104 and thetrunnion 106 are projected from the direction M in FIG. 21( a). In thisarrangement, the spherical shape of the outer face of each cylindricalprotrusion 106 a is viewed into an ellipse which is defined by thefollowing equations:

(X±Dc/2)²/(C/2)² +Y ²/(A/2)²=1   (1)

C=A sin Ω  (2)

Dc=Do cos Ω  (3)

where Dc represents the distance between the centers of the twoelliptical grooves, Do represents the base height between the twoopposing cylindrical protrusions, which is the entire height between thetwo opposing cylindrical protrusions minus the length of two sphericalsurface portions of the two opposing cylindrical protrusions, Arepresents a long diameter of the ellipse shape, which equals to thecylinder diameter of the cylindrical protrusions, C represents a shortdiameter of the ellipse shape, and Ω represents the inclining degree ofthe inner roller with respect to the trunnion. The hatched area S isdetermined by the ellipse shape represented by the equation (1) and aninner diameter d_(c) on the bottom portion of the inner roller 104, asan amount of interference between the bottom portion of the inner roller104 and each cylindrical protrusion 106 a. In other words, thecylindrical protrusion 106 a can be assembled into the inner roller 104without interference if the hatched area S of elliptical shape is carvedout from the bottom portion of the inner roller. FIG. 21( d) shows suchelliptical grooves formed on the bottom portion of the inner roller 104that is identical to the hatched area S shown in FIG. 21( c).

FIG. 21( e) illustrates a state that the inner roller 104 is returned toa normal position after the trunnion 106 was assembled into the innerroller 104 through the bottom grooves 104 b with the inner rollerinclined as described above. FIG. 21( f) is partial views of the innerroller and trunnion viewed from a direction of N shown in FIG. 21( e),in which the cylindrical protrusions 106 a are securely received in theelliptical grooves 104 b such that they can not be pulled out of thegroove 104 b under a normal operating condition since the cylindricalprotrusions 106 a have a height larger than the depth of the bottomgrooves 104 b of the inner roller 104, by the difference of Δr1 at thecenter to Δr2 at the edge ΦA. Accordingly, the grooves 104 b formed onthe bottom portion of the inner roller 104 as showed in FIGS. 21(a)-21(f), are provided not only to enable the trunnion 106 to be easilyassembled into the inner race 104, but also to prevent the trunnnion 106from pulling out of the inner roller 104 once it is assembled into theinner roller 104. Thus, the present embodiment is effective to reduce anextra manufacturing cost, such as a special tooling cost, typicallyrequired for the assembling methods in the previous embodiments asdiscussed above in connection with FIGS. 12-19.

With reference to FIGS. 22( a)-22(c), the thirteenth embodiment of thepresent invention is described herein. This embodiment is similar to thetwelfth embodiment described above. The difference of this embodimentfrom the above embodiment shown in FIGS. 20-21 is that each groove 104 bformed on the bottom portion of the inner roller 104 is composed of acircular groove portion with a diameter Φ H that coincides with theelliptically projected surface size of cylindrical protrusion 106 a at apoint Q and two peripheral planar groove portions with surface angle βformed tangential to the elliptically projected surface of cylindricalprotrusion 106 a at a point P as shown in FIGS. 22( a)-22(b). FIG. 22(c) depicts partial views of the inner roller 104 and trunnion 106 fromthe same direction N as shown in FIG. 21( e), in which the cylindricalprotrusions 106 a are securely received in the inner roller 104 so asnot to be pulled out of the grooves 104 b due to the oversizerepresented by the hatched area, since the cylindrical protrusions 106 ahave a size larger than the bottom groove 104 b of the inner roller 104,by the difference of Δ r1 at the center to Δ r2 at the edge Φ A.Accordingly, the bottom groove 104 b of the inner roller, as showed inFIGS. 22( a)-22(c), is provided not only to enable the trunnion to beeasily assembled into the inner race but also to prevent the trunnnionfrom disengaging out of the inner roller 104 once it is assembled intothe inner roller. Thus, this embodiment can also reduce the extramanufacturing cost required for the assembling process.

With reference to FIGS. 23( a) and 23(b), one preferred assemblingmethod of the tripod joints of the type shown in FIGS. 20-22 isdescribed herein. FIG. 23( a) includes explanatory and partial sectionalviews illustrating an initial arrangement made between the rollerassembly 112 and the trunnion 106 before fitting the roller assembly 112into the trunnion 106. The outer roller 103 is mounted on the shoulder107 a of a boss 107 of the tripod, in such a manner that a taperedcylindrical surface 103 a on the inner face of the outer roller 103 isconverged in the radial direction toward boss 107 of the tripod, withthe needle rollers 105 assembled into the tapered cylindrical surface103 a of the inner face of the outer roller 103. The inner roller 104 isplaced over the trunnion 106 of the joint such that a taperedcylindrical surface 104 a formed on the outer face of the inner roller104 is converged in the radial direction toward the boss 111. Then, theinner roller 104 is pushed to the trunnion 106 so that the cylindricalprotrusions 106 a (which are disposed in the direction receiving theload and protruded along the axis normal to the axis of the trunnion106) are partially fitted in the pair of bottom grooves 104 b of theinner roller 104 which are disposed in the direction receiving the load,as shown in FIG. 23( a). By this arrangement, some radial clearance ismaintained between the tapered outer cylindrical face 104 a of the innerroller 104 and the tapered inner cylindrical face 103 a of the outerroller 103 and the needle rollers 105. In this embodiment, the distanceD between the spherical end surfaces of two cylindrical protrusions 106a and the inner diameter Φd of the inner roller 104 is larger than theopening size H of the bottom groove 104 b of the inner roller, and theaxial length V1 of the groove 104 b is smaller that the distance fromthe bottom face to the center line of the inner roller 104.

FIG. 23( b) illustrates a method of assembling the roller assembly 112to the trunnion 106, to be performed after the previous steps discussedabove in connection with FIG. 23( a). While slightly pressing the innerroller 104 downwardly to maintain the partial engagement between theinner roller 104 and the cylindrical protrusions 106 a of the trunnion,the outer roller 103 (with the needle rollers assembled therein) islifted to the level of the inner roller 104, and thereby provides theroller assembly 112 which is positioned at the level of the partiallyengaged inner roller 104. Then, the roller assembly 112 (with the innerand outer rollers and the needle bearings assembled) is inclined ontothe trunnion 106 until the bottom 103 b of the outer roller contactswith the shoulder 107 a of the boss having height L. Here, in thisembodiment, the dimension of the elliptically projected surfaces of thetwo cylindrical protrusions 106 a is particularly designed to be stilllarger than the opening size H of the grooves 104 b formed on the bottomof the inner roller by Δ r1 on the center line of X1-X1. Then, a forceof predetermined amount (e.g., a force of manually applicable magnitudein that no equipment for the pressing is required) is applied on theupper side 103 d of the top portion of the outer roller, with the lowerside 103 c abutting against the shoulder 103 b of the boss, in order toallow a slight elastic expansion of the inner roller for easy assembly.Optionally, the inner roller may further include a pair of groovesformed on the top portion of the inner roller and in a directionperpendicular to the pair of grooves formed on the bottom portion of theinner roller in order to facilitate the elastic expansion of the innerroller about the pair of top grooves, as in the previous embodimentsshown in FIGS. 9 and 12, for example. Accordingly, this assembly methodcan reduce manufacturing or tooling cost typically required for theassembling process as in the previous embodiments described with FIGS.12-19.

With reference to FIG. 24( a) and FIG. 24( b), another preferredassembling method of the tripod joints of the type shown in FIGS. 20-22is described, in which FIG. 24( a) shows an explanatory viewillustrating an initial arrangement made between the roller assembly 112and the trunnion 106 before fitting the roller assembly 112 into thetrunnion 106, and FIG. 24( b) shows an explanatory view illustrating themethod of assembling the roller assembly 112 into the trunnion 106,which is performed after the arrangement shown in FIG. 24( a). Thisembodiment is similar to the previous method shown in FIG. 23( a) andFIG. 23( b). The difference of the present method from that shown inFIG. 23( a) and FIG. 23( b) is that the grooves 104 b on the bottomportion of the inner roller 104 are formed up to the center line of theinner roller, with the groove length V, and that the pair of cylindricalprotrusions 106 a of the trunnions are configured to have the heightbetween the two spherical end surfaces of the cylindrical protrusions106 a about the same (i.e., of less than 1 mm difference or allowing atypical machining tolerance) as an opening size between the pair ofgrooves. This makes the dimension of the elliptically projected surfacesof the opposing cylindrical protrusions 106 b to be smaller than theopening size H of the bottom grooves 104 b of the inner roller by thespace of −Δ r1 at the center line of X1-X1, when the inner roller 104 isinclined with respect to the trunnion 106 as the bottom 103 b of theouter roller abuts against the shoulder 107 a of the boss 107 havingheight L. Therefore, it enables the trunnion to be readily assembledinto the inner roller (which is inclined during the assembly process)without applying an external force of considerable amount typicallyrequired for the joint assembly as in the previous embodiments of FIGS.13-17, for example. Thus, the present embodiment can reduce the extramanufacturing cost typically required for the assembling process.

With reference to FIG. 25( a) and FIG. 25( b), another preferredassembling method of the tripod joints of the type shown in FIGS. 20-22is described, in which FIG. 25( a) shows an explanatory viewillustrating an arrangement made between the roller assembly 112 and thetrunnion 106 before fitting the roller assembly 112 into the trunnion106, and FIG. 25( b) shows an explanatory view illustrating the methodof assembling the roller assembly 112 into the trunnion 106, which isperformed after the arrangement shown in FIG. 25( a). This embodiment issimilar to the previous method shown in FIG. 23( a) and FIG. 23( b). Thedifference of the present method from that shown in FIG. 23( a) and FIG.23( b) is that the height L1 of the shoulder is smaller than that shownin FIGS. 23( a) and 6(b), and that the dimension of the ellipticallyprojected surfaces of the cylindrical protrusions 106 b is identical toor about the same as the opening size H of the bottom grooves 104 b ofthe inner roller 104 at the center line of X1-X1 when the inner roller104 is inclined onto the trunnion 106 until the bottom 103 b of theouter roller hits the shoulder 107 a of the boss 107 having height L1.Therefore, it enables the trunnion 106 to be readily assembled into theinner roller, without applying an external force of considerable amount,and thereby, reducing the extra manufacturing cost typically requiredfor the assembling process.

In the above embodiments described in connection with FIGS. 20-25, theprotrusions 106 a of the trunnions 106 have a cylindrical cross sectionand spherical end surfaces. However, they are not limited thereto, andthe protrusions 106 a can have an elliptical or oval cross section asillustrated in FIG. 8, or they may include a central recess portion asillustrated in FIG. 7. Similarly, the entire features described with theprevious embodiments associated with FIGS. 5-19 may also be adopted.

As described above with exemplary embodiments thereof, the tripod typeconstant velocity joint of the present invention utilizes trunnions eachhaving two diametrically projected, cylindrical projections of reducedsize, together with particularly adapted roller assemblies for suitablemating with the trunnions. Accordingly, the present invention canmaintain a low frictional spinning moment, and enables the rollerassembly to rotate smoothly without fluctuations, thus reducing theproblematic shudders typical in the vehicle operation. In addition, thepresent invention also provides effective methods of assembling theconstant velocity joint of the invention.

The above disclosed embodiments are representatives of a presentlypreferred form of the invention, but are intended to be illustrativerather than definitive thereof. Accordingly, those skilled in the artwill appreciate or recognize that various modifications andsubstitutions can be made thereto without departing from the spirit andscope of the present invention as set forth in the appended claims.

1. A constant velocity joint for a drive system having a first rotatingshaft and a second rotating shaft coupled with the constant velocityjoint, the constant velocity joint comprising: a hollow housing havingan opening at one end, and a closing at its opposite end fixed to an endof the first rotating shaft, an inner face of the housing including aplurality of guide grooves extending in an axial direction of thehousing and spaced equally apart in a circumferential direction of thehousing, each groove having a pair of side faces opposing to each other;a tripod disposed at an end of the second rotating shaft, having aplurality of trunnions each positioned in a corresponding one of theguide grooves and being spaced equally apart in a circumferentialdirection of and at an angle normal to the second rotating shaft; and aninner roller having a spherical inner face for receiving an outer endportion of each of the trunnions therein, an outer roller mounted on anouter face of each inner roller with needle rollers engaged between theinner and outer rollers, and allowing the outer face of each outerroller to roll and move in the corresponding one of the guide groovesand for transmitting a load between the first and second rotating shaftsto drive the driving system; wherein each of the trunnions includes apair of cylindrical protrusions opposingly disposed and protruded to adistance from an outer surface of the trunnion in a direction normal tothe axis of the trunnion, each of the cylindrical protrusions includinga spherical surface at its distal end for surface-to-surface contactwith the spherical inner face of the inner roller while defining a gaparound the cylindrical protrusion and between the surface of thetrunnion and the spherical inner face of the inner roller; wherein eachof the inner rollers includes a pair of grooves each formed in adiametric direction and on the bottom portion of the inner roller facinga boss of the tripod, the pair of grooves sized for receiving the pairof cylindrical protrusions of the trunnion while inclining the innerroller to a predetermined degree with respect to the trunnion forassembly.
 2. The constant velocity joint of claim 1, wherein each of thepair of grooves formed on the bottom portion of the inner roller has anelliptical groove shape corresponding to an elliptical shape of the pairof cylindrical protrusions when projected from the inner roller inclinedto the predetermined degree with respect to the trunnion.
 3. Theconstant velocity joint of claim 2, wherein the ellipse shape of thepair of grooves formed on the bottom portion of the inner roller aredefined by the equation of:(X±Dc/2)²/(C/2)² +Y ²/(A/2)²=1;C=A sin Ω;Dc=Do cos Ω; where Dc represents the distance between the centers of thetwo elliptical grooves, Do represents the base height between the twoopposing cylindrical protrusions, which is the entire height between thetwo opposing cylindrical protrusions minus the length of two sphericalsurface portions of the two opposing cylindrical protrusions, Arepresents a long diameter of the ellipse shape, which equals to thecylinder diameter of the cylindrical protrusions, C represents a shortdiameter of the ellipse shape, and Ω represents the inclining degree ofthe inner roller with respect to the trunnion.
 4. The constant velocityjoint of claim 2, wherein the cylindrical protrusions are securelyreceived in the elliptical grooves such that, after assembly, they cannot be pulled out of the grooves under a normal operating conditionbecause the cylindrical protrusions have a height larger than the depthof the bottom grooves of the inner roller.
 5. The constant velocityjoint of claim 2, wherein each of the inner rollers has a generallycylindrical outer surface tapered in an axial direction of the innerroller, and each of the outer rollers has a generally cylindrical innersurface tapered in an axial direction of the outer roller with the sametaper angle and in the same direction of the tapered outer surface ofthe inner roller, and wherein both the outer surface of said innerrollers and the inner surface of said outer rollers have said taperedsurfaces which are converged toward the boss of said tripod.
 6. Theconstant velocity joint of claim 1, wherein the gap around thecylindrical protrusion of the respective trunnion allows a lubricant tointroduce in the gap for lubrication.
 7. The constant velocity joint ofclaim 1, wherein the outer surface of each of the trunnions includes aspherical surface disposed in area subjecting to a load, and two flatsurfaces disposed in area not subjecting to the load and therebyproviding larger space between the flat surface and the spherical innerface of the respective inner roller, the space allowing a lubricant tointroduce therein for lubrication.
 8. The constant velocity joint ofclaim 1, wherein each of the grooves of the inner roller comprises acentral circular groove portion and two peripheral groove portionsdisposed lateral to the central circular groove portion.
 9. The constantvelocity joint of claim 9, wherein the central circular groove portionhas a radius defined by the elliptically projected surface size of thecylindrical protrusions and the two peripheral groove portions aregenerally planar with a taper angle tangential to the ellipticallyprojected surface of the cylindrical protrusions.
 10. A method ofassembling a roller assembly of a constant velocity joint onto atrunnion of the joint, comprising: providing a roller assembly for aconstant velocity joint, the roller assembly including: an outer rollerwith a tapered cylindrical surface formed on the inner face of the outerroller; an inner roller with a tapered cylindrical surface formed on theouter face of the inner roller and with at least partially sphericalinner face, the tapered outer cylindrical surface of the inner rollerhaving a same taper angle with the tapered inner cylindrical surface ofthe outer roller, the inner roller including a pair of groovesdiametrically disposed on a bottom portion of the inner face of theinner roller; and needle rollers for receiving between the inner andouter rollers; providing a constant velocity joint having a tripod withat least one trunnion, the trunnion including a pair of cylindricalprotrusions protruded normal to the axis of the trunnion to apredetermined height from an outer surface of the trunnion, each of thecylindrical protrusions having a generally spherical end surface forcontacting with the at least partially spherical inner face of the innerroller; mounting the outer roller on a shoulder portion of the tripoddisposed below the trunnion in such a manner that the tapered innercylindrical surface of the outer roller is converged in a radialdirection facing a boss of the tripod, the outer roller having theneedle rollers assembled in the tapered inner cylindrical surface of theouter roller; placing the inner roller onto the trunnion and partiallyintroducing the pair of cylindrical protrusions of the trunnion in thecorresponding pair of grooves formed on the bottom portion of the innerroller; tilting the inner and outer rollers with one side of the outerroller abuts against the shoulder portion of the trunnion such that oneof the pair of cylindrical protrusions is thoroughly received in theinner face of the inner roller through a corresponding one of the pairof grooves of the inner roller and the other one of the pair ofcylindrical protrusions is still partially introduced in the other oneof the pair of grooves of the inner roller, and allowing the inner andouter rollers to be inclined by a predetermined degree with respect tothe trunnion; and pushing an upper side of the inclined outer rollerdown to the shoulder portion of the trunnion until the other one of thepair of cylindrical protrusions is completely received in the inner faceof the inner roller through the other one of the pair of grooves of theinner roller.
 11. The method of claim 10, wherein said providing theroller assembly step and said providing the constant velocity joint stepprovide the inner roller having the pair of grooves each with an axiallength smaller than a distance from the bottom face of the inner rollerto the center line of the inner roller, and provide the trunnion havingthe pair of cylindrical protrusions with a distance between the twospherical end surfaces of the pair of cylindrical protrusions largerthan an opening size between the pair of grooves and with a distancebetween the two spherical end surfaces of the pair of cylindricalprotrusions, when projected from the axis of the inner roller inclinedby said tilting step, still larger than the opening size between thepair of grooves; and wherein said pushing step is performed whileapplying a force of predetermined amount on the upper side of theinclined outer roller with a lower side of the inclined outer rollerabutting against the shoulder portion of the trunnion for allowing anelastic expansion of the inner roller for assembly.
 12. The method ofclaim 11, wherein the inner roller includes a pair of grooves formed onthe top portion of the inner roller and in a direction perpendicular tothe pair of grooves formed on the bottom portion of the inner roller forfacilitating the elastic expansion of the inner roller about the pair ofgrooves formed on the top portion of the inner roller.
 13. The method ofclaim 10, wherein said providing the roller assembly step and saidproviding the constant velocity joint step provide the inner rollerhaving the pair of grooves each with an axial length about the same as adistance from the bottom face of the inner roller to the center line ofthe inner roller, and provide the trunnion having the pair ofcylindrical protrusions with a distance between the two spherical endsurfaces of the pair of cylindrical protrusions about the same as anopening size between the pair of grooves and with a distance between thetwo spherical end surfaces of the pair of cylindrical protrusions, whenprojected from the axis of the inner roller inclined by said tiltingstep, smaller than the opening size between the pair of grooves; andwherein said pushing step is performed without applying an externalforce of considerable amount on the upper side of the inclined outerroller with a lower side of the inclined outer roller abutting againstthe shoulder portion of the trunnion for assembly.
 14. The method ofclaim 10, wherein said providing the roller assembly step and saidproviding the constant velocity joint step provide the inner rollerhaving the pair of grooves each with an axial length smaller than adistance from the bottom face of the inner roller to the center line ofthe inner roller, and provide the trunnion having the pair ofcylindrical protrusions with a distance between the two spherical endsurfaces of the pair of cylindrical protrusions larger than an openingsize between the pair of grooves and with a distance between the twospherical end surfaces of the pair of cylindrical protrusions, whenprojected from the axis of the inner roller inclined by said tiltingstep, about the same as the opening size between the pair of grooves;and wherein said pushing step is performed without applying an externalforce of considerable amount on the upper side of the inclined outerroller with a lower side of the inclined outer roller abutting againstthe shoulder portion of the trunnion for assembly.